panfrost: signal syncobj if nothing is going to be flushed
When nothing is going to be flushed, the kernel will get no job that signals the syncobj. Signal it by ourselves, otherwise it will never get signaled. Closes: #3371 Signed-off-by:Icenowy Zheng <icenowy@aosc.io> Reviewed-by:
Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com> Cc: mesa-stable Part-of: <!6190> (cherry picked from commit 9e397956)